The present invention relates to circuits and methods for controlling load sharing by multiple power supplies. More particularly the present invention relates to circuits and methods for controlling load sharing by multiple power supplies that use a voltage loop that monitors a current loop and that provide detection and hot-swapping capabilities.
When using multiple power supplies to supply power to a load, it is frequently desirable and necessary to split the power provided to the load evenly among the multiple power supplies. One way in which this is done is through the use of load share controllers which monitor the output current of each power supply. In these controllers, load sharing is achieved by determining which power supply is providing the highest amount of current and increasing the current provided by the remaining power supplies to just under that amount.
Although such known load share controllers provide the ability to split a load evenly among multiple power supplies, these controllers suffer from various inadequacies. For example, these power supplies exhibit low frequency ripple that is caused by controlling load sharing based only upon the current output of the supplies. As another example, such power supplies can experience catastrophic failure conditions when the current provided by one power supply increases out of regulation and the remaining power supplies attempt to match that current.
Thus, it is an object of the present invention to provide load share controllers that provide improved load sharing performance, fault detection, and hot-swapping capabilities.
In accordance with this and other objects of the invention, circuits and methods for controlling load sharing by multiple power supplies are provided. In preferred embodiments of the invention, load share controllers utilize multiple voltage control loops to monitor the output voltages that are being provided by multiple power supplies connected to a load. These voltage control loops each generate a voltage control voltage that is proportional to the difference between the actual output voltage of the corresponding power supply and the desired output voltage. The voltage control loop with the highest voltage control voltage then controls a current control voltage generated in a current control loop for each power supply via a share bus. These current control loops then regulate the current provided by the corresponding power supplies so that those currents are all proportional to the voltage on the share bus.
By monitoring the current control voltage in each current control loop, the voltage at the output of each power supply, and the direction of the current flowing between each power supply and the load, the circuits and methods of preferred embodiments of the invention can detect and account for out-of-regulation conditions, over voltage conditions, short circuit conditions, and hot-swapping conditions. In the event of these conditions, the preferred embodiments of the invention provide an indication of the condition at a status pin and attempt to minimize the harmful effects that may be created.